{"id":248299,"date":"2026-09-01T08:43:35","date_gmt":"2026-09-01T07:43:35","guid":{"rendered":"https:\/\/www.marbre-import.fr\/?page_id=248299"},"modified":"2026-09-01T08:43:35","modified_gmt":"2026-09-01T07:43:35","slug":"diagnosis-stained-darkened-stone-facades-runoff-marks","status":"publish","type":"page","link":"https:\/\/www.marbre-import.fr\/en\/natural-stone-encyclopedia\/diagnosis-stained-darkened-stone-facades-runoff-marks\/","title":{"rendered":"Diagnosis: Stained or Darkened Stone Fa\u00e7ades and Runoff Marks"},"content":{"rendered":"

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Home<\/a> \/ Natural Stone Encyclopedia<\/a> \/ Diagnosis: Stained, Blackened or Run-Off-Marked Stone Fa\u00e7ades<\/strong><\/div>\n
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Diagnosis by Symptom<\/p>\n

Diagnosis: Stained, Blackened or Run-Off-Marked Stone Fa\u00e7ades<\/h1>\n

Read the pattern of soiling to distinguish run-off, pollution, corrosion, microorganisms, salts, coping defects and migration from joints or fixings.<\/p>\n

\n Open the interactive tool<\/a>Ask a stone specialist<\/a>\n <\/div>\n<\/p><\/div>\n<\/section>\n
\"Natural-stone<\/a>
Natural-stone fa\u00e7ade: joints, edges and water management \u2014 Diagnosis of staining, darkening and runoff marks<\/figcaption><\/figure>\n
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Identify the condition before treating it<\/h2>\n

The shape of a runoff mark often reveals its origin. A streak below a coping differs from a halo around a fixing, darkening beneath a cornice or biological growth in a damp, shaded area.<\/p>\n

Map the staining and inspect the construction details before cleaning. A clean fa\u00e7ade that remains poorly drained will soil again quickly, sometimes with even stronger contrasts.<\/p>\n

\n\n\n\n\n\n\n\n\n\n
Observed sign<\/th>\nWhat it may indicate<\/th>\nFirst action<\/th>\n<\/tr>\n<\/thead>\n
Vertical streaks below a coping<\/td>\nConcentrated runoff or a missing drip<\/td>\nCorrect the detail<\/td>\n<\/tr>\n
Orange halo around a fixing point<\/td>\nCorrosion of a fixing or adjacent metal<\/td>\nPrioritise a safety check<\/td>\n<\/tr>\n
Dark deposits beneath sheltered areas<\/td>\nPollution deposits deposits not washed by rain<\/td>\nIdentify the deposit and stone<\/td>\n<\/tr>\n
Green or brown growth in a damp area<\/td>\nAlgae, moss or biofilm<\/td>\nReduce moisture and shade where possible<\/td>\n<\/tr>\n
White deposits around joints<\/td>\nSalts and moisture migration<\/td>\nTrace the path from behind the stone<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/section>\n
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Using the shape of a mark as a diagnostic tool<\/h2>\n

A streak beginning directly below a joint or fixing indicates a probable source. Diffuse wind-oriented soiling suggests exposure. A clear difference between rain-washed and sheltered bands shows the combined effect of rainfall and pollution.<\/p>\n

Cleaning trials should recover an appropriate texture and colour without opening the stone surface or creating an isolated over-cleaned patch that cannot be blended.<\/p>\n<\/section>\n

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\n \"Diagnostic
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The shape of a mark guides diagnosis: a streak below a coping, a line beneath a sill, a halo at a joint, an orange trace near a fixing and a dark area beneath an overhang do not have the same causes. Trace the water path, inspect copings, drips, sills, joints, drainage and metals, then correct the detail before cleaning a sample panel. Select the image to enlarge it.<\/figcaption><\/figure>\n
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Checks that will not make the condition worse<\/h2>\n
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Check<\/th>\nHow to proceed<\/th>\nHow the result informs the diagnosis<\/th>\n<\/tr>\n<\/thead>\n
Photographic mapping<\/td>\nFull elevation and located close-ups<\/td>\nLinks staining with fa\u00e7ade elements<\/td>\n<\/tr>\n
Inspection of copings and parapets<\/td>\nCopings, joints, drips and edges<\/td>\nIdentifies runoff paths<\/td>\n<\/tr>\n
Fixing inspection<\/td>\nBy a specialist where metal staining or movement is present<\/td>\nRules out dangerous corrosion<\/td>\n<\/tr>\n
Deposit sampling<\/td>\nWhere crusts, salts or biological growth are uncertain<\/td>\nInforms the cleaning method<\/td>\n<\/tr>\n
Test panels<\/td>\nGraduated pressure, water, chemistry and contact time<\/td>\nConfirms the result and degree of surface loss<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/section>\n
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Step-by-step diagnosis<\/h2>\n
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Stage<\/th>\nQuestion to resolve<\/th>\nDecision<\/th>\n<\/tr>\n<\/thead>\n
1<\/td>\nDoes the mark indicate a fixing problem or falling hazard?<\/td>\nMake the area safe and obtain specialist advice<\/td>\n<\/tr>\n
2<\/td>\nIs a detail concentrating the water?<\/td>\nRepair it before final cleaning<\/td>\n<\/tr>\n
3<\/td>\nIs the deposit biological, mineral, metallic or pollution-related?<\/td>\nSelect a targeted method<\/td>\n<\/tr>\n
4<\/td>\nCan the stone tolerate the method?<\/td>\nTest texture and colour<\/td>\n<\/tr>\n
5<\/td>\nHow can the fa\u00e7ade be blended without over-cleaning?<\/td>\nDefine boundaries and acceptance criteria<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/section>\n
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Treat the confirmed cause<\/h2>\n
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Confirmed cause<\/th>\nTreatment principle<\/th>\nCondition for success<\/th>\n<\/tr>\n<\/thead>\n
Runoff<\/td>\nCorrect the coping, joint, drip or drainage<\/td>\nTest under rain or controlled water exposure<\/td>\n<\/tr>\n
Pollution deposits<\/td>\nProgressive cleaning suited to the deposit and stone<\/td>\nApproved sample panel<\/td>\n<\/tr>\n
Biological growth<\/td>\nCompatible treatment followed by moisture reduction<\/td>\nControlled contact time and rinsing<\/td>\n<\/tr>\n
Corrosion<\/td>\nRepair or replace the metal and address migration<\/td>\nDesign and compatibility confirmed<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/section>\n
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What not to do<\/h2>\n